3rd Generation Partnership Project (3GPP), one of a number of mobile communication standardization organizations, is engaging in a Long Term Evolution (LTE) standardization process and an advanced LTE standardization process in order to develop a packet based mobile communication system standardization. A mobile communication system generally includes a base station constituting a cell, and a mobile terminal used by a user. A plurality of mobile terminals may transmit and receive packet data to and from the base station via a radio channel.